Resilient article and alloy and their manufacture



Patented Sept. 26, 11%

RESlLlENT ARTICLE AND ALLoY AND rnnm MANUFACTURE 1 Robert B. Wasson, Cranford, N. J., and Alfred V. dc Forest, Cambridge, Mass., assignors to John Chatillon & Sons, New York, N. Y., a corporation of New York No Drawing. Application February 14,-l936, Serial No. 63,892. Renewed July 12, 1939 t 18 Claims.

This invention relates to the production of resilient metallic articles and to an improved alloy and method of treating the same particularly useful in the production of such articles wherein elasticity is an important factor in the desired performance. The invention is especially useful in the production of springs, such as helical or platform or cantilever springs, but is also useful in others of a variety of applications wherein the elastic properties are important.

Elastic behavior is dependent upon a number of factors, principal among which arethe change in coeflicient of modulus of elasticity and change in the coefficient of linear or bulk expansion, oocasioned by change intemperature; creep of the metal under continued load well within the elastic limit, followed generally by gradual elastic recovery after removal of load; variation in performance upon repeated use and long standing; and hysteresis of the metal as exhibited by failure to follow the same deflection curve under increasing and decreasing loads.

In accordance with the conditions of service peculiar to any particular application of a resilient metallic element, one or more of the above named factoraassumes greater or lesser importance.

It is an object of the present invention to provide anew alloy and procedure for treating the same. It is also an object to provide an alloy and procedure for treating the same. which are particularly adapted to the production of metallic elements which closely approach true elasticity and which manifest the optimum elastic properties with respect to the particular uses to which they are to be put. Another object is to provide an alloy and procedure for treating the same wherein high elastic. limits and a greater range of elastic behavior may be obtained throughout a range of temperatures. It is also an object to provide an alloy and method of producing the same wherein greater ultimate tensile strength and yield point and greater stability (repetition of performance upon reuse orlong standing) may be obtained. Another object is to obtain an alloy or article of improved torsional elasticity and capable of withstanding great torsional stresses. A further object is to provide springs and other resilient metallic articles having improved characteristics. Other objects willbecome apparent.

In utilizing our invention in its preferred form, a nickel-iron alloy of particular composition is selected and this composition is subjected to a specific sequence oi physical and heattreatments,

depending to some extent upon the particular use to which the article is to be put.

, The following is an example of an embodiment of the invention in the production of helical springs for measuring weights and forces, although it is not intended to restrict the invention to this particular use or to the specific examples or procedures described, it being apparent that many modifications may be made in order to utilize the invention in various ways.

The following is an alloy which may be used to advantage for this purpose, the percentages used herein being by weight:

. Percent Carbon .10 Nickel- 36.0 Chromium 7,75 Manganese 0.65 Molybdenum 0.50 Silicon. 0.50 Copper- 3 .2

Sulphur and phosphorus -As low as practical Iron Balance The elements included in the above alloy may be varied somewhat, the following being an indication of somewhat wider ranges suitable for this use: v

The proportions and elements may be varied somewhat, as hereinafter indicated, but it is preferred to maintain the nickel between to 36% The iron present will be over and usually about 50 to 60%, depending upon the other elements used. The carbon content should be kept as low as possible, .10% or less being preferred.

The above alloy may be melted or cast at about 2850" F. and hot worked starting at about 2100- F., after which it may be annealed for about 3 to 4 hours at about 1750 F.

This preliminary heat treatment of the alloy may be varied considerably, the important consideration being to treat it in such a manner as cles.

' rials.

to provide a grain size suitable for the high degree of cold working hereinafter described.

After the alloy is annealed it may be heavily cold worked, for example, to about 7% of its original cross sectional area, for example, as by drawing it through a series of dies in the well-known manner of wire drawing. For instance, the annealed alloy may have a diameter of about which diameter may be reduced to about .140" in the wire drawing operation, giving a final area of cross section or about 6.2% of the initial area of cross section or a reduction in area of cross section of about 93.8%. i

This degree of cold working is important in producing the desired results but may be varied somewhat. For example, in the production of larger wires a lower degree of reduction in cross section, for instance, to 88%, may be sufficient. With finer wires a reduction in cross section of 99% or even more may be desired. In general it is preferred to reduce the cross section at least After the material has been cold worked to the degree indicated above and the final desired shape is given to it, the helical spring may be sublected to heat at about 750 F. for about 20 minutes to stabilize it. This final heat treatment may be conducted at somewhat higher temperatures for a shorter time, as discussed more fully hereafter, although such higher temperatures may result in a reduction in the elastic limit of the metal, an undue amount of which is undesirable where high elastic limits are required. The final heat treatment may also be conducted at lower temperatures for a longer time, for example, at 600 F. for 4 to fi'hours, although it is obvious that a commercial advantage may be gained by avoiding such long time treatment.

By the unusually great degree of cold working described above when applied to this particular type of alloy, the physical characteristics are greatly improved; for example, the tensile strengthis increased and the elastic limit is in creased.

By using the above described alloy and following the procedure described, a helical spring may be made having a modulus of elasticity which is substantially unaffected by change in temperature throughout a wide range and the coefllcient of linear expansion of which is considerably reduced as compared to prior known spring mate-- With a stress in torsion of 60,000 pounds per square inch applied to such an alloy, the creep or the alloy is reduced to less than .02% of the deflection. The accompanying hysteresis is not over .02 to .04% of the full load deflection. A spring of higher ultimate tensile strength and yleld point and of greater stability and improved torsional elasticity and of greater resistance to torsional stresses may be obtained.

Materials having these characteristics can be advantageously substituted for the materials previously used in the production of numerous arti- For example, when the material is formed into Bourdon tubes or into metallic bellows or Sylphons, the elastic properties, of these devices are considerably improved, not only because this material is substantially unaifected by temperature change and has a. higher elastic limit, but in both of these devices when other materials are used there is a difference in the deflection curve as between loading and unloading. By improving our material with respect to hysteresis, as stated above, this undesirable performance with respect to the deflection curve has been substantially eliminated. The alloy is also not sensitive to season crac Other advantageous characteristics of the material are its ductility, malle-' ability, and resistance to corrosion by various chemicals and liquids. For example, it may be used directly in contact with mercury or ammonia since it is substantially inert to these substances. It also is highly resistant to various acids and alkalis and may be used where it may come into contact with these. I

As indicated above the elements and treatment of the alloy may be varied considerably in utilizing the invention. The nickel-iron relationship of about that indicated above is important, but in order to obtain the desired hardness, tensile strength and working properties, other elements are also important. The'presence of chromium,

for example, or some other element which acts in a similar manner, is important since it tends to keep the modulus of elasticity constant. With the proper balance of the other elements this may be varied, for example, from 5 to 10%. The molybdenum is important to give the desired degree of hardening and it or some other element which acts in a similar manner should be added in quantities such' that it, together with the other elements present, will give a solid solution at the annealing temperatures (about 1600-2000 F.) but willgive precipitation or age hardening upon reheating to temperature 01' about 400 F. to

1000 F. Other elements, such as tungsten, ti-

'tanium, vanadium, cobalt, uranium or tantalum,

may be used as the hardening agent, with or in place of the molybdenum or chromium.

The manganese adds fluidityto the alloy and is important in the casting of the alloy since it helps to avoid the presence of blow holes. It also is of value in obtaining, the desired degree of malleability of the alloy. More than 315% manganese might be used, but inthat event the quantity of chromium should be reduced; The-sulphur and phosphorus should be kept as low as possible to obtain the best cold working properties.

The important consideration in the selection of the elements and their proportions is to provide an alloy which may be cold worked to the degree desired without intermediate heating, and which will give precipitation or age hardening during the aging or stabilizing heat treatment after the somewhat less than that required to give the maximum hardness when measured as Rockwell hardness. i

In the ultilization oi the alloys referred to above in the production of other articles than helical springs,some variations in the procedure from the specific example given above may be desirable to give the required characteristics. For example, in the production of hair springs for watches, it is desirable to subject the finished article to a more extensive final heat treatment in order to set the spring. For instance, a minimum heat treatment of 4 hours at 1000 F., or for a shorter time at a higher temperature (for example, up to about 1300-1350 F.) is desirable for this purpose. This more extensive heat treatment tends to reduce the elastic limit of the spring and in order to compensate for this it is desirable to increase. the cold working of the alloy, for example, to about 99% of its initial area of cross section.

It is quite obvious, therefore, that a somewhat different treatment may be followed in the production of different articles. Where increased stability is required in order to obtain repeated uniiorm performanceoi' the article, for example, as in a hair spring, this greater stability is obtained by increasing the final heat treatment. This increased stabilizing treatment reduces the elastic limit, but this reduction may be compensated for at least to a considerable extent by increasing the degree of cold working. In the production of helical springs, high elastic limit is important and the degree of stability is not so important.

In the production of tuning forks from the above alloy, it is desirable to subiect'the final article to a somewhat higher temperature than that of the specific example above, for a shorter time. For example, improved results have been obtained using a stabilizing temperature of about The shape of the tuning fork is such that the high degree of cold working may be commercially impracticable. In any event improved results may be obtained by the selection of the particular alloy described and the subsequent stabilizing treatment referred to above.

It is obvious that other applications of the invention may be made and that in many instances other variations in procedures may-be necessary. For example, the improvement may be used in the production of springs for gauges in pressure instruments, in the production of diaphragm springs for altimeters, in the produc-' tion of reeds for organs, in the production of Bourdon tubes and of bellows type of volume expansible tubes for thermostatic and pressure control systems and in the production of elements for radio oscillators or clocks and other time keeping devices.

- In certain articles it may be desirable not to have a zero temperature coeillcient of the modulus of elasticity. For example, with certain geometric shapes a' temperature coeillcient otherthan zero may be desirable to compensate for changes due to bulk'expansion or contraction of the article. This temperature coeflicient may be varied somewhat by'the cold working and aging or stabilizing operations, although it is very dinicult to absolutely control this characteristic in,

The terms used in describing the'invention have been used in their descriptive sense and not as terms of limitation, it being intended that all equivalents of the terms used be included within the scope of the appended claims.

We claim: 1. In the preparation of a nickel-iron alloy spring material having substantially a zero temperature coemcient of the elastic modulus, the

steps of providing an alloy containing about 5 about 4 hours at 1000 F.

- manganese, .35 to .65% molybdenum, .30 to .60%

and cold working the alloy to reduce its area of cross section by about 90 to 99.9%.

2. In the preparation 01 a nickel-iron alloy, the steps of providing an alloy containing about 35 to 37% nickel, 50 to 60% iron, 7 to 8% chlO- mium, .45 to 15% manganese, .35 to .65% molybdenum, .30 to .60% silicon and not over 2% carbon in an annealed condition, cold working the alloy to reduce its cross section by over about 85%, and heating the finished article to bring about a hardening of the alloy.

3. A spring having a low temperature coefficient of elastic modulus composed of an alloy comprising about 34.5 to 37% nickel, 'l to chromium, .45 to .75% manganese, .35 to 55% molybdenum, .30 to .60% silicon, not'over about .2% carbon and the balance substantially all iron, said alloy having been cold worked to reduce its area of cross section by over 85%.

4. A helical spring having a low temperature coeiiicient of elastic modulus composed of an alloy comprising about 34.5 to 37% nickel, 7 to 8% chromium, .45 to 35% manganese, .35 to 65% molybdenum, .30 to .60% silicon, not over about .2% carbon, and the balance substantially all iron, said alloy having been annealed, cold worked to reduce its area of cross section by over 85%, iorm'ed and heat stabilized.

5. A helical spring having a low temperature 6. A hair spring having -a low temperature coefllcient of elastic modulus composed of an alloy comprising about 34.5 to 37% nickel, 7 to 8% chromium, .45 to 175% manganese, .35 to .65%'molybdenum, .30 to .60% silicon, not over about .2% carbon and the balance substantially all iron, said alloy having been annealed, cold worked to reduce its area of crosssection by more than 85%, and heat treated at a"temperature of 400 to 1300 F. to improve the properties thereoi without eliminating the effect of the cold working.

7. A hair spring having a low temperature coefliclent of elastic modulus composed of an alloy comprising about 34.5 to 37% nickel, '1 to 8% chromium, .45 to .75% manganese, .35 to .65% molybdenum, .30 to .60% silicon, not over about 2% carbon and the balance substantially all iron, said alloy having been cold worked to reduce its area of, cross section by over 98% and the formed spring having been'heat stabilized for 8. A volume expansible element having a low temperature coefficient of elastic modulus composed oian alloy comprising about 34.5 to 37% nickel, '7 to 8% chromium, .45 to .'75% mancon, not over about 2% carbon and about to iron, saidvalloy havingbeen annealed, cold worked to reduce its 'area of cross-section by more than 85%, and heat treated at a temperature of 400 to 1300" F. to improve the properties thereof without eliminating the eilect oi the cold work ganese, .35 to'.65% molybdenum, .30 to .60% 5111- 10. A metallic bellows havingm. low temperature coefileient or elastic modulus composed of an alloy comprising about 34.5'to 37% nickel,

'7 to 8% chromium,-.45 to 175% manganese; .35 to .65% molybdenum, .30 to-.60% silicon, not over about .2% carbon and 50 to 60% iron, said alloy having been annealed. cold worked to reduce its area of .cross-section by, more than 85%, and heat treated at a temperature or 400 to 1300 F. to improve the properties thereof without eliminating the effect of the cold working.

11. In the preparation of a helical spring, the steps comprising providing an alloy containing about 35.5 to 36.5% nickel; to 8% chromium. .45 to 375% manganese, .35 to 55% molybdenum, .30 to .60% silicon, not over about .10% carbon and the balance substantially all iron, annealing and cold working said alloy to reduce its area or cross section by over 90%, forming it into the shape of a helical spring and heat stabilizing the h'ggcal spring for about 20 minutes at about '7 F.

12. A resilient member having a low temperature coei'iicient of elastic modulus composed of an alloy comprising about 34.5 to 37% nickel. 7 to 8% chromium, .45 to 35% manganese, .35 to .65% molybdenum, .30 to .60% silicon, and not over about .2% carbon and 50 to 80% iron, said alloy having been annealed, cold worked to reduce its area 0! cross-section by more than 85%, and heat treated at a temperature of 400 to 130 F. to improve the properties thereof without eliminating the eiiect oi the cold working.

13. A heattreated cold worked article oi! manuiacture having a high elastic limit and a low temperature coemcient of elastic modulus and containing at least 50% iron, about 34.5 to 7% nickel, to 10% chromium, not more than about .2% carbon, and a hardening agent oi! the group consisting of molybdenum, tungsten, titanium. vanadium, cobalt, uranium, and tantalum, said article having been annealed at a temperature of about 1600 to 2000 21"., cold worked to reduce its area or cross section by more than about 8 and hardened by heating to a temperature above about 400 F. but not substantially above 1300" F.

4. A heat treated cold worked article of manufacture having a high elastic limit and a low temperature coemcient of em modulus and containing at least 50% iron, about 34.5 to 37% nickel, 5 to 10% chromium, not more than about .2% carbon, and about .35 to 65% molybdenum, said article having been annealed at a temperaiture of about 1600 to 2000 3!, cold worked to reduce its area 01' cross section by more than about 85%, and hardened by heating to a temperature above about 400 F. but not substantially above 1300 F.

15. In the preparation of material having a high elastic limit and a low temperature coeflicient of elastic modulus, the steps of heating a ferrous alloy containing 50 to 60% iron, about 35 to 87% nickel, about 5 to 10% chromium, carbon in an amount not greater than about 0.2%

and, a hardening element of the group consisting of molybdenum, tungsten, titanium, vanadium, cobalt, iranium and tantalum, to an annealing temperature of about 1600 to 2000" F., cold working said annealed alloy to reduce its area or cross-section by more than about 85%, and reheating said cold worked alloy to a temperature above about 400 'F. but not substantially above 1300 F. to modify the elastic properties thereof without eliminating the effect oi cold working. r

16. In the preparation 01 material having a high elastic limit and a low temperature coefilferrous alloy containing 50 to 60% iron, about carbon in an amount not greater than about 0.2% and a small proportion .01 molybdenum as a hardening element, to an annealing temperature of about 1600 to 2000 K, cold working said cient of elastic modulus, the steps of heating a -25 35 to 37% nickel, about 5 to 10% chromium,

. annealed alloy to reduce its area of cross-section by more than about 85%, and reheating said cold worked alloy to a temperature above about 400 F'. but not above 1300" F. to modify the elasticiproperties thereof without eliminatin! the eil'ect of cold working.

17. Ahelical spring having a high elastic limit and a lofwtemperature coeiiicient of elastic modulus composed of an alloy containing at least 0! iron, about 34.5 to 37%nickel. 5 to 10% ohm.-

mium, a sufliciently small amount of carbon to permit severe cold working, and a hardening agent or the group consisting of molybdenum,

tungsten, titanium, vanadium, cobalt, uranium and tantalum, said spring having been annealed, 5

by at least about and stabilized by reheating to a temperature not substantially above 1300' F.

18. In a force measuring apparatus, a spring for measuring substantial weights or forces composed or an alloy of high elastic limit and low temperature coeflicient of elastic modulus, said alloy containing at least 50% or iron, about 34.5

cold worked to reduce its area of cross section to 37% nickel, 5 to 10% chromium,a' suiliciently 5 small amount of carbon to permit severe cold working, and a hardening agent 01 the group consisting of molybdenum, tungsten, titanium, vanadium, cobalt, uranium and tantalum, said-spring having been annealed, cold worked to reduce its area of cross section by at least about 85%, and stabilized by reheating to a temperature not substantially above 1300 1".

- ROBERT LB. WASSON.

ALFRED V. 1:: FOREST. 

